Japanese Patent Application No. 2000-98766, filed on Mar. 31, 2000, is hereby incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a surface emitting semiconductor laser which emits laser light in a direction perpendicular to a semiconductor substrate, and a method of manufacturing the surface emitting semiconductor laser.
2. Description of Related Art
A surface emitting semiconductor laser is a semiconductor laser which emits laser light in a direction perpendicular to a semiconductor substrate, with a resonator provided on a semiconductor substrate in a direction perpendicular to the semiconductor substrate. This resonator generates then emits the laser light, and comprises a reflecting layer, active layer, and reflecting layer, in that order.
Outstanding characteristics that can be cited of a surface emitting semiconductor laser compared with an end-surface laser, are that the direction of laser emission is uniform, and can be made small, and it therefore provides high efficiency coupling of optical elements. A surface emitting semiconductor laser therefore holds great promise in application as a light source particularly in optic fiber communications using for example terminal large-diameter core optic fiber.
In terminal optic fiber communications, it is required for the structure of an optical transmission module to be simplified, for the installation to be made easier, and for the cost to be reduced. Since a surface emitting semiconductor laser is suited to a large-diameter core optic fiber, such as for example a plastic optic fiber or the like, and the method may be considered in which no lens is provided between the optic fiber and the light source, and the laser light is emitted directly into the optic fiber, to improve the optical efficiency. By this method, since the laser light can be emitted efficiently into the optic fiber, an optical transmission module of extreme simplicity can be realized.
However, plastic optic fibers have the drawback that the light losses are large, and when a long transmission path is required, a light source with a high power laser light output is required. As one means of increasing the laser light output of a surface emitting semiconductor laser may be cited an increase in the laser light emission aperture. However, if the laser light emission aperture is made larger, the problem occurs that the laser light emission angle increases. An increase in the laser light emission angle invites a loss of coupling efficiency and a decrease in the fitting margins, and this makes it difficult to simplify the structure of an optical communications module. That is to say, it has been difficult to achieve the twin aims of ensuring the transmission distance, while simplifying the structure of the optical communications module.
The objective of the present invention is the provision of a surface emitting semiconductor laser and method of manufacturing the surface emitting semiconductor laser, such that a high laser output is obtained, and the laser emission angle is narrow.
(A) According to the present invention, there is provided a surface emitting semiconductor laser which has a resonator formed on a semiconductor substrate in a direction perpendicular to the semiconductor substrate, to emit laser light from the resonator in a direction perpendicular to the semiconductor substrate, wherein:
a pillar-form semiconductor deposition is provided in at least part of the resonator;
an emission portion having a convex lens form is formed on an upper surface of the semiconductor deposition;
the semiconductor deposition has an embedded structure, and is embedded in an embedding layer; and
the embedding layer is formed from a substance having non-affinity with a material used to form the emission portion.
By a substance having non-affinity with the material used to form the emission portion is indicated a substance whose properties are such as to repel the material used to form the emission portion. Therefore, the material used to form the emission portion has low wettability with respect to the substance.
As the substance having non-affinity with the material used to form the emission portion may be cited an inorganic material or a resin. For example, in the case of a resin, a fluorine-based resin can be used.
By means of this structure, a high laser output can be obtained, and the laser emission angle of the surface emitting semiconductor laser can be made narrow. This is described in more detail in the embodiments of the present invention.
This surface emitting semiconductor laser has some features as shown by following examples (1) to (3).
(1) An electrode which supplies current to the resonator may be formed on the upper surface of the semiconductor deposition.
In this case, the electrode may be formed of a metal.
(2) The diameter of the emission portion in a plane of adhesion of the semiconductor deposition and the emission portion, and the diameter of the upper surface of the semiconductor deposition may be substantially equal. By means of this structure, since the diameter of the emission portion in the plane of adhesion of the semiconductor deposition and the emission portion can be made equal to the diameter of the upper surface of the semiconductor deposition, particularly for surface emitting semiconductor lasers formed in an array, emission portions of matching sizes can be formed. Since the diameter of the upper surface of the semiconductor deposition and the diameter of the emission portion in the plane of adhesion of the semiconductor deposition and the emission portion substantially coincide, the optical axis of the emission portion, and the axis passing through the center of the semiconductor deposition and perpendicular to the upper surface of the semiconductor deposition substantially coincide. Further, the optical axis of the emitted laser light is substantially coincident with the axis passing through the center of the semiconductor deposition and perpendicular to the upper surface of the semiconductor deposition. Therefore, the optical axis of the emission portion, the optical axis of the laser light, and the axis passing through the center of the semiconductor deposition and perpendicular to the upper surface of the semiconductor deposition substantially coincide, as a result of which a surface emitting semiconductor laser with little deviation from the optical axis can be obtained.
(3) The emission portion may be formed of a polymer compound.
(B) According to the present invention, there is provided a method of manufacturing a surface emitting semiconductor laser comprising the steps of:
(a) forming a resonator including a pillar-form semiconductor deposition on a semiconductor substrate;
(b) forming an electrode which supplies current to the resonator in a state with a predetermined region of an upper surface of the semiconductor deposition exposed;
(c) forming an embedding layer around the semiconductor deposition to give the semiconductor deposition an embedded structure by embedding the periphery of the semiconductor deposition in a substance having non-affinity with a liquid which is used to form an emission portion having a convex lens form by curing;
(d) disposing the liquid on the upper surface of the semiconductor deposition; and
(e) curing the liquid to form the emission portion.
The liquid refers to the material used to form the emission portion, and by a substance having non-affinity with the liquid is indicated a substance whose properties are such as to repel the liquid. That is to say, the liquid has the property of low wettability with respect to the substance.
According to this method, the periphery of the semiconductor deposition is embedded in the substance having non-affinity with the liquid, whereby an embedding layer is formed on the periphery of the semiconductor deposition, and the resonator is given an embedded structure, while further, by simply supplying the liquid to the upper surface of the semiconductor deposition, and curing the liquid, the emission portion functioning as a microlens can be formed by self-alignment. That is to say, there is a large difference in the wettability by the liquid of the upper surface of the semiconductor deposition and the surface of the embedding layer, whereby the liquid is spontaneously formed by surface tension into a convex lens form, and by curing this an emission portion having the form of a convex lens can be obtained. As above, with the surface emitting semiconductor laser of the present invention, since the emission portion can be formed with self-alignment, a laser emission portion requiring no alignment of the optical axis, and with no deviation from the optical axis can be formed by a process of extreme simplicity.
In the process, the substance may be a resin.
In this case, as the resin a fluorine-based resin may be used. A fluorine-based resin has non-affinity with almost any type of resin liquid. On the other hand, the semiconductor layer or electrode surface of the surface emitting semiconductor laser has affinity with almost all types of resin liquid. As a result, by using a fluorine-based resin, a large difference between the wettability of the upper surface of the semiconductor deposition by the liquid and the wettability of the surface of the embedding layer formed of the resin by the liquid can be achieved, and the liquid can be caused to adhere only to the upper surface of the semiconductor deposition. As a result, the size can be controlled, and an emission portion can be obtained with even less deviation from the optical axis.
In step (d), as the means of supplying the liquid to the upper surface of the semiconductor deposition, the following two methods can be cited by way of example.
In the first method, a drop of the liquid is formed on a tip of a dispenser nozzle, and the drop is contacted with the upper surface of the semiconductor deposition, whereby the liquid is disposed on the upper surface.
According to this method, by using the nozzle, the viscosity of the liquid, the nozzle bore, and the drop size on the tip of the nozzle can be adjusted, surface treatment can be applied to the nozzle tip, and so on, so that the thickness of the emission portion can easily be controlled. The method of supply of the liquid by a nozzle is not susceptible to the influence of the viscosity of the liquid, and therefore the range of liquids that can be used is wider. Further, since the liquid is positively supplied only to where it is required, and therefore waste is eliminated, and liquid does not adhere to places in which it is not required.
In the second method, by using an inkjet head the liquid is ejected to the upper surface of the semiconductor deposition, thus disposing the liquid on the upper surface.
By means of this method of using an inkjet head, the liquid can be supplied to the surface in a short time, which provides the characteristic of high productivity.
In the above process, the liquid may include a thermosetting resin, ultraviolet cured resin, or a precursor of the thermosetting resin or ultraviolet cured resin.